Preferred embodiments of the present invention relate to the placement of an electronic element, such as a resistor or diode in an end plug of the terminal end of the sensing edge (i.e., the end which is not connected to the control mechanism for the motor of the automatic door). The input end of the sensing edge is the end which is connected to the control mechanism. Sensing edges for automatic doors are generally well known. A description of sensing edges can be found, for example, in U.S. Pat. No. 6,571,512, titled “Universal Sensing Edge with Non-Melt End Closure,” and which disclosure is incorporated by reference herein in its entirety.
Sensing edges generally include an elongated sheath configured to sense force. Upon an application of a force to the sheath, the elongated sheath actuates suitable control circuitry for controlling movement of a door. For example, an automatic door can have a sensing edge on a leading or bottom edge. If an object is below the elongated sheath, the elongated sheath is pressured by the object when the automatic door impacts the object when closing. Such force is “sensed” by the elongated sheath, which results in a predetermined signal being sent to a mechanism which opens or closes the automatic door to cause the automatic door to stop moving to prevent damage to the object or the door.
One way for the elongated sheath to sense force is to have first and second spaced apart electrically conductive materials extending in a longitudinal direction of the elongated sheath. The electrically conductive materials are electrically connected, on an input end of the sensing edge, to the control circuitry which controls the movement of the door. The other end (i.e., the terminal end) of the electrically conductive materials is often not electrically connected to anything, and the electrically conductive materials are often not connected to each other at the terminal end. Thus, there is no closed circuit, and therefore no electricity flows through the electrically conductive materials. Once force is applied to the elongated sheath, it causes the first and second electrically conductive materials to connect to each other, closing the circuit and allowing current to flow. The control circuitry, or other device connected to the control circuitry, senses the change from having no current flowing, to having current flowing, signaling that the automatic door has engaged an object which has put pressure on the elongated sheath. The control circuitry then stops or opens the automatic door.
A problem with the above system is that in the “standby” mode of operation, no current is flowing through the electrically conductive materials. Thus, if the system is damaged, such as, for example, by at least one of the electrically conductive materials being cut, the system may not be able to carry a current even if pressure is applied to the elongated sheath. The control circuitry then “senses” that no current is flowing and takes no action to stop or close the automatic door, even if an undesired object has been engaged. One technique for solving this problem is disclosed in U.S. Pat. No. 5,345,671, titled “Process of Making a Sensing Edge With a Failsafe Sensor,” the disclosure of which is incorporated by reference herein in its entirety. In this technique, the terminal end is connected to an electronic component (resistor, diode or the like), such that the electronic component electrically connects the first and the second electrically conductive materials together, thereby providing three possible current states (e.g., no current, low current and high current).
Such systems typically include the electronic component beyond an end plug of the sensing edge, and the electrically conductive materials must be electrically connected with the electronic component. Accordingly, it is desirable to more simply and efficiently add an electronic component to the sensing edge circuit.